In the image forming apparatus using electrophotographic process, images are formed to recording media, etc. by processes of charging, irradiation, development, transfer etc. applied to an image bearing member. A minute amount of corona products produced in the charging process and/or residual toner remaining after the transfer process are attached to the surface of the image bearing member after the transfer process and these attached matters are removed by the cleaning process after the transfer process. Thereafter, another image is formed again on the image bearing member from the charging process.
A cleaning system having a rubber blade is typically used in the cleaning process because such a rubber blade has a simple and cost-saving mechanism with a good cleaning property. However, since the rubber blade is pressed against the image bearing member to remove the attached material on the surface thereof, the rubber blade and the image bearing member are under a large mechanical stress caused by friction between the surface of the image bearing member and the rubber blade. This easily leads to attrition of the rubber blade and the surface layer of the image bearing member, which shortens the working life of the rubber blade and the image bearing member. This attrition is significant particularly on the surface layer of an organic photoconductor. On the other hand, the toner for use in image formation is reduced in size to deal with the demand for improvement on the image quality. In the case of an image forming apparatus using a toner having a small particle diameter, the ratio of residual toner that slips through the edge portion of the cleaning blade and the surface of the image bearing member tends to increase. This is particularly true when the dimension accuracy and/or assembly accuracy is not sufficient or the cleaning blade partially vibrates, which prevents formation of quality images. Therefore, reducing the deterioration of the image bearing member and the cleaning blade caused by abrasion and improving the cleaning property of the surface of the image bearing member are demanded to elongate the working life of the image bearing member while maintaining the quality of images over a long period of time. To meet this demand, a protection agent (lubricant) is applied to the surface of an image bearing member to form a film layer of the protection agent thereon.
The protection agent applied to the surface of an image bearing member reduces the abrasion on the surface of the image bearing member caused by the friction between the cleaning blade and the image bearing member and/or the deterioration of the image bearing member caused by the discharging energy generated when the image bearing member is charged in the charging process. In addition, the protection agent applied to the surface of an image bearing member increases the lubricant property thereof, thereby reducing the partial vibration of the cleaning blade. Therefore, the amount of toner that slips through the cleaning blade in the cleaning process is reduced. However, the lubricant property and the protection property depend on the amount of the protection agent. An amount of the protection agent that is excessively small does not sufficiently demonstrate prevention effects on the attrition of the image bearing member, the deterioration of the image bearing member caused by AC charging, and the slip-through of toner. Therefore, there are disclosed image forming apparatuses in which the amount of a protection agent applied to the surface of the image bearing member is specified.
For example, an unexamined published Japanese patent application No. (hereinafter referred to as JOP) 2004-198662 describes an image forming apparatus in which an amount of zinc stearate (metal soap) applied to the surface of the image bearing member as a protection agent is specified by the ratio of zinc to all the elements detected by X-ray photoelectron spectroscopy (XPS) analysis on the surface of the image bearing members. In addition, X-ray fluorescence (XRF) analysis is used to specify the application amount of the protection agent to maintain the quality of images over an extended period of time. Image forming apparatuses diffused nowadays are normally capable of forming color images and the quality images are demanded. Thus, the dominant charging system currently employed uses a charging roller applying an AC voltage in which an AC voltage is overlapped with a DC voltage to the surface of the image bearing member. Furthermore, the AC charging system using a charging roller deals with the need for size reduction, produces less amount of oxidized gasses such as ozone and NOx and naturally is expected to be widely and continuously used in the future. However, an image bearing member is charged several hundreds to several thousands of times per second according to frequency when the AC charging system is used. Thus, the image bearing member is easily and heavily damaged in the AC charging system in comparison with a DC charging system in which an image bearing member is positively charged only once while the image bearing member passes through the charging device. Therefore, protecting the image bearing member from damage caused by charging is demanded in the AC charging system. In addition, since resource saving has been drawing a high attention recently, elongating the working life of each member and part is an issue. As described above, since the speed of deterioration of the image bearing member is fast in the AC charging system in comparison with the DC charging system, the typical method of protecting an image bearing member is insufficient and thus a new protection technology is demanded. Furthermore, when a metal soap is used, part of powder of the metal soap supplied to the image bearing member is known to slip through the cleaning blade, scatter and attach to the charging roller, which degrades charging. Mixing an inorganic lubricant such as mica and boron nitride with a metal soap instead of a simple use of the metal soap is known to be effective to avoid this problem. JOP 2008-134467 describes a technology in which mica or boron nitride is blended with a metal soap (zinc stearate) to reduce scattering of the metal soap to the charging roller and the abrasion of the cleaning blade for an extended period of time. In addition, JOP 2006-350240 describes a technology of supplying boron nitride to an image bearing member as a protection agent and demonstrates that since discharging hardly affect the characteristics of boron nitride in comparison with other lubricants such as metal soap, boron nitride prevents oxidization deterioration of the image bearing member by discharging and works as a good protection agent for the image bearing member.
The present inventors made a study about improvement on the protection function of the metal soap used as a protection agent for an image bearing member while varying the amount of the metal soap with reference to JOP 2004-198662. However, the present inventors have found that an increase in the amount of the metal soap leads to an excessive increase of the volume of the installed metal soap, which is against the needs of the size reduction. In addition, abrasion of the cleaning blade is inevitable in the long run even if a large amount of metal soap is installed. Therefore, while a great number of images are formed in total, the cleaning blade is abraded. Thus, the working life of the cleaning blade is not elongated although the working life of the image bearing member is elongated. To the contrary, when the amount of metal soap is too small, the abrasion of the image bearing member tends to be significant or components of toner easily attaches to the image bearing member, which may cause an adverse impact on the quality of images. Thus, reducing the amount of metal soap is not preferable, either. In addition, as described in JOPS 2008-134467 and 2006-350240, the protection agent mixed with mica and/or boron nitride covers the shortcomings described above. Judging from specific Examples, good results are obtained when the protection agent contains mica and/or boron nitride in a relatively large amount, i.e., from 40 to 80%. However, mica and boron nitride are inorganic material having a high hardness. Attachment of a large amount of such an inorganic material to the surface of the image bearing member tends to accelerate the attrition of the cleaning blade. On the other hand, restriction on the supply amount of the protection agent leads to a decrease of the supply amount of metal soap. Consequently, a suitable protection layer is not formed on the surface of the image bearing member and thus, the problems described are left unsolved.